1. Field of the Invention
The present invention relates to a structure for fixing a permanent magnet used in a motor.
2. Description of the Related Art
DC motors in which a permanent magnet is used in a stator and a coil is used in a rotor (armature) are proposed. Generally, a permanent magnet is fixed inside a housing by using an adhesive. Various methods of fixing are proposed. For example, the inner circumferential surface of the side wall of a case may be coated with an adhesive. By inserting a permanent into the case, spreading the adhesive by using the end of the permanent magnet, the adhesive is spread between the outer circumferential surface of the permanent magnet and the inner circumferential surface of the case. Thus, the permanent magnet can be fixed at a desired position (see patent document 1). As a method of manufacturing a permanent magnet used in a stator, there is proposed a method of manufacturing a ring-shaped bonded magnet by injecting a molten resin member that contains magnetic powder (see patent document 2).
[patent document 1] Published Utility Model Application 62-168711 [patent document 2] JP2009-137138
If there is a difference in linear expansion coefficient between the permanent magnet, the case, and the adhesive, the permanent magnet will undergo a stress due to a change in the temperature, which could result in a crack in the permanent magnet. In the case that the inner circumferential surface of the case is coated with an adhesive before inserting the permanent magnet, a portion of the adhesive is dragged in the direction of insertion due to the movement of the end face or lateral face of the permanent magnet. It would therefore be difficult to ensure a uniform amount of adhesive coating over the entirety of the space between the inner circumferential surface of the case and the outer circumferential surface of the permanent magnet.